Most television broadcasts are interrupted by publicity breaks that include commercial advertisements and other promotional segments. While these interruptions are received with irritation by many television viewers, in other situations many viewers want to view the advertisements. Viewers may want to view advertisements for entertainment, consumer information, or competitive intelligence purposes, for example. There are therefore at least two reasons to identify and extract segments from broadcast television signals: to eliminate publicity breaks from a broadcast program, or to store the advertisements for later viewing.
While automated procedures for identifying segments (including commercial advertisements) from broadcast signals for both of these purposes, are well known in the art, known procedures are generally inefficient, and relatively unreliable. One of the primary reasons for extracting the segments is to be able to identify rebroadcast segments. While it is well known in the art to provide signatures derived from an audio and/or a video portion of the broadcast signal, known methods of re-identifying broadcast segments need improvement.
Warren D. Moon teaches generating a signature for a broadcast signal in his U.S. Pat. No. 3,919,479, entitled BROADCAST SIGNAL IDENTIFICATION SYSTEM, which issued on Nov. 11, 1975. The signature is generated by sampling a low-frequency envelope of a predetermined size generated from a non-linear analog transform of the audio and video components of the broadcast signal, and digitizing the samples. Unfortunately the number of samples required to characterize the segment makes the signature cumbersome to match, and expensive to store.
Subsequently alternative procedures for generating smaller signatures have been developed that, unfortunately, poorly characterize segments. A number of patents have taught signatures generated from one or only a few frames of the segment. Given the imprecise methods available for defining when a frame begins, identification of a first frame in the segment is not reliable, consequently an obvious difficulty arises in identifying those particular frames in the broadcast signal so that the comparison is made correctly. For example, U.S. Pat. No. 6,002,443, entitled METHOD AND APPARATUS FOR AUTOMATICALLY IDENTIFYING AND SELECTIVELY ALTERING SEGMENTS OF A TELEVISION BROADCAST SIGNAL, which issued to Iggulden on Dec. 14, 1999, teaches the use of an average luminance value of select lines of a select frame of the segment. More specifically, 64 consecutive odd lines chosen after line 22 of an NTSC frame, of a 10th frame after a segment transition event, are suggested for this purpose. The suggested signature is a small 64-bit value, one bit defined by each respective line, in relation to a threshold. While the signature is 64 bits long, it does not characterize more than the one frame of the segment.
Running Moon's system intermittently, upon detection of segment transitions, has been suggested, but, as is noted in U.S. Pat. No. 4,677,466, entitled BROADCAST PROGRAM IDENTIFICATION METHOD AND APPARATUS, which issued to Lert Jr. et al. on Jun. 30, 1987, stability of the broadcast signal needs to be assessed before the signature can be generated. Otherwise a risk of misidentifying the chosen frames of the segment may lead to errors. Stability testing is a computationally expensive procedure involving detection of segment transitions and scene changes by comparing average luminance values of successive frames. Apart from this complexity, which Lert's system bears, one or even a few frames are not adequate to characterize a segment. Some broadcast segments are minor variants of others, such as “donut ads”, which are identical except for one or more frame sequences. Failure to differentiate these segments is not desirable in many cases. Particularly for competitive intelligence purposes, an advertiser's reuse of advertising content may be of interest.
Another method of generating a signature for a broadcast segment is taught in U.S. Pat. No. 5,436,653 entitled METHOD AND SYSTEM FOR RECOGNITION OF BROADCAST SEGMENTS, which issued to Ellis on Jul. 25, 1998. The signature generation method taught by Ellis involves calculating a difference vectors from average luminance values of pairs of predefined patches of pixels (both active and blanked) of the frame. There are 16 pairs of the patches, and consequently 16 difference values are calculated (by subtraction, for example) for each frame. Each of the 16 value difference vector is subjected to a plurality of vector transformations to yield the signature. While meritorious, the method requires complicated video edge detection, sophisticated vector transformation algorithms designed to improve the differentiation of the resulting signatures, and jitter compensation to adaptively modify a portion of the patches used to generate the averages. It is not clear how segments are delimited with enough precision to accurately identify the frames that are to be used for signature generation. While the invention does provide a relatively compact signature (assuming that relatively few frames are used for matching), the signature constructed is only representative of a few frames.
None of the prior art systems characterize a broadcast segment using features relating to its entire length while providing a reasonably-sized signature. Further, known systems fail to reliably distinguish two segments that have similar frame sequences, and misidentify common frame sequences in different segments. There therefore remains a need for a system that is largely immune to a broadcast signal's noise, jitter and instability, that efficiently and accurately characterizes substantially entire segments, and can be reliably used to identify common frame sequences in different broadcast segments.